Swiatek had 22 winners in the clash to Pegula's 14, and she finished with only three more unforced errors than the American.
The match finished at 2:49 a.m., which has also set the record for the longest duration US Open match ever played.
In a two-hour, 26-minute encounter marred by rain, Rublev won 6-4, 6-4, 6-4, gaining crucial breaks in all three sets to emerge victorious.
Right from the start, the 21-year-old Italian felt out of place with 14 double faults and managed to put just 46 per cent of first serves into play.
Playing for a spot in the quarterfinals, the players kept coming back at each other to provide the spectators with an absolute spectacle of a match.
The top-ranked Swiatek was tested in the match but she stepped up during crucial moments to equal her best performance at the season-ending Grand Slam. The Pole had also reached the fourth round last year.
The 21-year-old, free-swinging Swiatek, a two-time Grand Slam champion, is showing signs that she might be prepared to reach such heights once more.
Despite being the second youngest player left in the women’s draw, 18-year old Gauff remains as one of the favorites to win the US Open title along with top-ranked Iga Swiatek.
On Wednesday at Arthur Ashe Stadium, Williams defeated World No. 2 Anett Kontaveit 7-6(4), 2-6, 6-2 in front of yet another boisterous, uproarious record crowd.
This was Nadal’s first US Open Match since he clinched the Grand Slam title back in 2019.
